1. Technical Field
The present inventions relate to switching power converters and, more particularly, relate to controllers for switching power converters employing pulse width modulation and electromagnetic interference reduction.
2. Description of the Related Art
Switched-Mode DC to DC converters generate and suffer from switching noise and electromagnetic interference (EMI). This problem is frequency sensitive. Distributing the switching frequency over a wider frequency spectrum is known to help to mitigate the effects from switching noise and electromagnetic interference.
One way that the switching frequency gets distributed over a wider frequency spectrum is when there is a noisy quantization clock. A dirty or noisy clock, for example, the 2 GHz clock in a laptop is not steady so it does not produce a pure 2 GHz tone. But this is not by design, just by accident. A noisy clock is not a very well controlled emission.
Another way uses a clean clock to count off a different number of cycles as in U.S. Pat. No. 7,130,346, issued Oct. 31, 2006 to Midya et al., entitled “Method and apparatus having a digital PWM signal generator with integral noise shaping.”